I haven't been able to spend a lot of time going through everything yet today, but I've tried a few DivX movies and I can confirm that they work now. If you were streaming with TVersity before, you can skip it entirely now and play your movies without any hassles, burned or not.
Also, there's a selection of free themes and gamerpics out today for the Xbox Originals. I've only checked out the Crimson Skies one, but it was surprisingly good. Anyone know whether these will always be free, or if they are just free for today?